Do they exist in the game? Can't find buy them from any trainers and I can't find anything on them on the wiki pages.

In my sickening amount of time spent playing the game I don't think I've seen either. That doesn't mean they don't exist but it's safe to say that at best they're exceedingly rare. I've found a set of dragonplate armor but never an expert or master hood.

High Level mages seem to wear circlets in Skyrim. I personally like the look of Blue Robes and Alik'r Hoods for my mage character. I get them from Radiant Raiments in Solitude. I am not too fond of the way Archmage robes look on me.

According to UESP/personal experience, they don't exist.

Well that just doesn't make any damn sense.